Yesterday, while I was cleaning my one year old Messor colony (queen caught October 2017) I noticed a massive ant I had never seen before. It was about 1 cm long (if not more) and had a orange head (different from the red color I usually see on majors). I only spotted one in the whole nest that big and there are about 300 ants in it.

Could have they produced a supermajor already in their first year or may it be only a oversized major?

Not sure, but I know for about the first year the worker ants are much smaller than they will be later. Also the ant size depends on how much they were fed as larvae. So if you provide them with ample food you will get bigger workers than if you just provide them with minimum food. Perhaps this major got a lot more food than the previous majors did.

Ive seen this with my tetramorium colony. It is producing workers almost twice the size of the workers that it produced in the first year.

Now that I think about it yes, I've fed them a lot and different kind of proteins in the past months such as mealworms, crickets, roach pieces, spiders and so on. Doing so I managed to understand what they prefer so next year, when the population will be booming, I'll know what to rely on.